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COMPUTED TOMOGRAPHY
Impact of an advanced image-based
monoenergetic reconstruction algorithm on coronary stent
visualization using third generation dual-source dual-energy CT:
a phantom study
Stefanie Mangold
1,2
&Paola M. Cannaó
1,3
&U. Joseph Schoepf
1,4
&
Julian L. Wichmann
1,5
&Christian Canstein
6
&Stephen R. Fuller
1
&
Giuseppe Muscogiuri
1,7
&Akos Varga-Szemes
1
&Konstantin Nikolaou
2
&
Carlo N. De Cecco
1,7
Received: 25 February 2015 / Revised: 18 May 2015 / Accepted: 1 September 2015 /Published online: 15 September 2015
#European Society of Radiology 2015
Abstract
Purpose To evaluate the impact of an advanced
monoenergetic (ME) reconstruction algorithm on CT coro-
nary stent imaging in a phantom model.
Materials and methods Three stents with lumen diameters of
2.25, 3.0 and 3.5 mm were examined with a third-generation
dual-source dual-energy CT (DECT). Tube potential was set
at 90/Sn150 kV for DE and 70, 90 or 120 kV for single-energy
(SE) acquisitions and advanced modelled iterative reconstruc-
tion was used. Overall, 23 reconstructions were evaluated for
each stent including three SE acquisitions and ten advanced
and standard ME images with virtual photon energies from 40
to 130 keV, respectively. In-stent luminal diameter was
measured and compared to nominal lumen diameter to deter-
mine stent lumen visibility. Contrast-to-noise ratio was
calculated.
Results Advanced ME reconstructions substantially increased
lumen visibility in comparison to SE for stents ≤3 mm.
130 keV images produced the best mean lumen visibility:
86 % for the 2.25 mm stent (82 % for standard ME and
64 % for SE) and 82 % for the 3.0 mm stent (77 % for standard
ME and 69 % for SE). Mean DLP for SE 120 kV and DE
acquisitions were 114.4± 9.8 and 58.9 ± 2.2 mGy × cm,
respectively.
Conclusion DECT with advanced ME reconstructions im-
proves the in-lumen visibility of small stents in comparison
with standard ME and SE imaging.
Key Points
•An advanced image-based monoenergetic reconstruction al-
gorithm improves lumen visualization in stents ≤3.0 mm.
•Application of high keV reconstructions significantly im-
proves in-stent lumen visualization.
•DECT acquisition resulted in 49 % radiation dose reduction
compared with 120 kV SE.
Keywords Dual-energy CT .Coronary CT .Stent .
Monoenergetic imaging .Iterative reconstruction
Abbreviations
CCTA Coronary computed tomography
DECT Dual-energy computed tomography
keV kilo-electron volts
ME Monoenergetic
CNR Contrast-to-noise ratio
*U. Joseph Schoepf
schoepf@musc.edu
1
Division of Cardiovascular Imaging, Department of Radiology and
Radiological Science, Medical University of South Carolina, Ashley
River Tower, 25Courtenay Drive, Charleston, SC 29425-2260, USA
2
Department of Diagnostic and Interventional Radiology,
Eberhard-Karls University Tuebingen, Tuebingen, Germany
3
Scuola di Specializzazione in Radiodiagnostica, University of Milan,
Milan, Italy
4
Division of Cardiology, Department of Medicine, Medical University
of South Carolina, Charleston, SC, USA
5
Department of Diagnostic and Interventional Radiology, University
Hospital Frankfurt, Frankfurt, Germany
6
Siemens Medical Solutions, Malvern, PA, USA
7
Department of Radiological Sciences, Oncology and Pathology,
University of Rome BSapienza^, Rome, Italy
Eur Radiol (2016) 26:1871–1878
DOI 10.1007/s00330-015-3997-4
SE Single-energy
ECG Electrocardiogram
CTDI
vol
Volume-based computed tomography dose index
Introduction
Non-invasive diagnostic workup of patients with coronary
computed tomography (CCTA) after coronary artery stenting
is still a challenging task, as blooming artefacts caused by
beam hardening and partial volume effects impair stent visu-
alization and result in underestimation of the stent lumen.
While innovations in cardiac CT technology have led to high
negative predictive values for exclusion of in-stent restenosis
from 78 to 100 %, positive predictive values are markedly
inferior, ranging between 18 and 89 % [1]. Thanks to technical
improvements in image acquisition and post-processing, sev-
eral new approaches to enhance the evaluation of coronary
stent patency and in-stent stenosis have been developed. In
particular, new iterative reconstruction algorithms and the
use of high convolution kernels have recently shown promis-
ing results [2–8].
Another promising approach to improve image quality is
dual-energy CT (DECT) acquisition, which enables the gen-
eration of virtual monochromatic images at different virtual
kilo-electron volt (keV) levels [9–13]. Using single-source
DECT, Stehli et al. were able to show that monoenergetic
(ME) reconstructions from DECT acquisitions improve stent
lumen visualization [14]. Recently, an advanced image-based
ME algorithm (Dual Energy Monoenergetic Plus, Siemens,
Forchheim, Germany) was introduced, which utilizes a
frequency-based mixing of low keV images that provides a
higher contrast signal and images from the keV level optimiz-
ing image noise. Thus, the images generated combine the
benefits of both image stacks while overcoming the noise
limitations associated with the standard ME technique (Dual
Energy Monoenergetic, Siemens), allowing for significantly
improved iodine contrast-to-noise ratios (CNR) in comparison
to standard ME images and single-energy (SE) acquisitions
[11–13].
The aim of this study was to comprehensively evaluate the
impact of the advanced ME reconstruction algorithm on stent
imaging in comparison to standard ME reconstructions and
SE acquisition in a moving coronary stent phantom with
third-generation dual-source DECT.
Materials and methods
Stents and phantom setup
Three commercially available drug-eluting stent systems,
which are commonly used in clinical practice for percutaneous
coronary intervention, were studied (Taxus Express
2
with in-
ner diameters of 3.0 mm and 3.5 mm; Taxus Express
2
Atom
with inner diameter of 2.25 mm; Boston Scientific Corpora-
tion, Natick, MA, USA). All stents were made of 316 L stain-
less steel with a strut wall thickness of 0.132 mm. Before
being imaged, each stent was implanted on an identical poly-
urethane tube of a defined outer diameter (2.25, 3.0, and
3.5 mm), which served as a contrast-enhanced vessel speci-
men with an attenuation of 200 HU (CTIodine, QRM Quality
Assurance in Radiology and Medicine GmbH, Moehrendorf,
Germany). The artificial vessels were fixed in a specimen
holder and positioned in a water-filled polymethyl methacry-
late container held in place by a lever attached to a motion
simulator (Motion Simulator Sim2D, QRM). The container
was then placed in position of the heart in an anthropomorphic
thoracic phantom resembling a human chest (Cardio CT Phan-
tom, QRM). The movement of the lever was controlled by a
computerized controller module, which simulated a bi-
directional cardiac motion in the stent phantom, while gener-
ating a synchronous ECG signal (Fig. 1).
CT acquisition parameters
All examinations were performed with a third-generation du-
al-source DECT scanner (SOMATOM Force, Siemens)
equipped with a fully integrated circuit detector system (Stel-
lar Infinity, Siemens). Images were acquired with prospective-
ly electrocardiogram (ECG)-triggered acquisition at 70 % of
the RR interval using a simulated ECG from the cardiac mo-
tion phantom with a heart rate of 70 beats per minute and sinus
rhythm. The scan parameters were as follows: detector colli-
mation 2×64×0.6 mm for DE acquisition and 2× 68 × 0.6 for
SE acquisition, gantry rotation 0.25 s, 512× 512 pixel matrix
size, 190 mm reconstruction field of view. Tube potential was
Fig. 1 Experimental set-up with a moving coronary stent phantom sim-
ulating a bi-directional cardiac motion while generating a synchronous
ECG signal
1872 Eur Radiol (2016) 26:1871–1878
set at a combination of 90 kVand 150 kV with tin filtration for
DECT and 70, 90 and 120 kV for SE DSCT. Automated tube
current modulation (CAREDose 4D, Siemens) was enabled
for DE and SE and automated tube potential selection
(CAREkV, Siemens) was set in Bsemi^mode in order to main-
tain constant iodine contrast to noise ratio (CNR) for the SE
scans [15]. The volume-based computed tomography dose
index (CTDI
vol
) was automatically provided by the system
and tube current and dose length product (DLP) were recorded
for each acquisition.
Image reconstruction and analysis
All SE and DE images were reconstructed with a third-gener-
ation, advanced modelled iterative reconstruction algorithm
(ADMIRE, Siemens) with strength 3 using a medium sharp
convolution kernel (Bv49), 0.5 mm section thickness, and
increment of 0.3 mm.
Using dedicated post-processing software (Syngo.via
VA30 Dual Energy, Siemens) advanced and standard ME re-
constructions were enabled with virtual photon energies of 40,
50, 60, 70, 80, 90, 100, 110, 120, and 130 keV. Overall, 23
image series were evaluated for each stent including three SE
acquisitions and ten advanced and standard ME images, re-
spectively, using the same post processing system. For each
stent and image, reconstruction in-stent luminal diameter was
measured manually on cross section images at three different
levels using the electronic diameter calipers provided by the
workstation’s software. The reviewer was blinded to the ap-
plied image reconstruction and stent lumen diameter and a
zoomed field of view with a fixed window level at 300 HU
and window width of 1200 HU was used. Stent lumen visi-
bility was calculated as the ratio of manual measurements of
the stent lumen and nominal lumen diameter of the stent,
given in percent.
For measurements of attenuation, circular regions of inter-
est (ROI) were placed within the stent, carefully avoiding the
stent components and blooming artefacts. ROIs were also
placed in the carrier tube outside the stent as well as the water
inside the phantom. Image noise was defined as the standard
deviation (SD) of the attenuation in the surrounding water.
Measurements were performed on three different sections of
each stent and given as mean values. CNR was calculated as
the difference of attenuation of in-stent iodine solution and
attenuation of water divided by image noise.
Statistical analysis
Commercially available software (MedCalc Statistical Soft-
ware, v12.7.5.0, MedCalc bvba, Belgium) was used for statis-
tical analysis. For all numerical values derived from multiple
measurements, the mean value and standard deviation (SD)
were calculated. Lumen visibility and objective image quality
parameters (noise and CNR) were plotted against tube poten-
tial. Dose reduction for low SE and DE tube potential acqui-
sitions was calculated using the 120-kV acquisition on the
same CT system as the reference standard.
Results
Measurement values for mean stent lumen, mean lumen visi-
bility, attenuation of the carrier tube within sections inside and
outside the stented area, image noise, and CNR are given in
Tab le 1for selected keVand kV levels. Objective image qual-
ity parameters (noise and CNR) plotted against tube potential
for each stent are provided in Fig. 2with representative CT
images in Figs. 3,4and 5.
Attenuation, noise and CNR evaluation
In terms of objective image quality, advanced ME reconstruc-
tions provided increased CNR values in comparison to stan-
dard ME images and SE acquisitions (Table 1, Fig. 2). The
highest CNR was found for the advanced ME reconstruction
at 120 keV with a value of 8.1 for 2.25 mm, 6.5 for 3 mm, and
5.8 for 3.5 mm diameter stents. The maximum CNR for stan-
dard ME images was 3.9 at 70 keVand 5.6 at 120 keV with SE
acquisition.
Lumen diameter evaluation
In advanced ME reconstructions, the in-stent diameters were
substantially increased in comparison to standard SE images
and slightly increased in comparison to the standard ME re-
construction algorithm for the 2.25 mm and 3.0 mm stent. The
highest values for lumen visibility werefound for 130 keVand
advanced image based ME reconstructions with a lumen vis-
ibility of 82 % for the 3.0 mm stent (77 % for standard ME
images and 69 % for SE acquisition) and of 86 % for 2.25 mm
diameter stent (82 % for standard ME images and 64 % for SE
acquisition). For 3.5 mm stents, the improvements in stent
lumen visibility were less pronounced with mean values of
92 % for advanced ME images, 91 % for standard ME recon-
structions and 87 % for SE acquisitions (Table 1, Fig. 2).
Radiation dose
SE image acquisition with a tube voltage of 120 kV, 90 kV,
and 70 kV resulted in a mean CTDI
vol
of 12.0± 2.4, 5.6±0.7
and 3.8± 1.0 mGy as well as a DLP of 114.4± 9.8, 59.7±6.1,
and 36.5±1.9 mGy× cm, respectively.
The DE acquisition resulted in a mean CTDI
vol
of 5.5±
0.7 mGy and a DLP of 58.9± 2.2 mGy×cm, which represents
a 49 % reduction in comparison with the standard 120 kV SE
acquisition (Fig. 6).
Eur Radiol (2016) 26:1871–1878 1873
Tab l e 1 Mean stent lumen, mean lumen visibility), attenuation values of the tube inside and outside the stented area as well as noise values and contrast-to-noise ratio (CNR) for selected kiloelectron
(keV) and kilovolt levels (kV)
40 keV
Mono+
70 keV
Mono+
90 keV
Mono+
120 keV
Mono+
130 keV
Mono+
40 keV
Mono
70 keV
Mono
90 keV
Mono
120 keV
Mono
130 keV
Mono
70 kV
Standard
90 kV
Standard
120 kV
Standard
2.25 mm
Stent lumen (mm) 1.3± 0.2 1.6± 0.2 1.7 ± 0.1 1.9 ± 0.1 1.9 ± 0.2 1.2 ±0.2 1.5±0.2 1.7±0.1 1.8± 0.1 1.8 ± 0.1 1.3 ± 0.1 1.5±0.2 1.4±0.1
Mean lumen visibility (%) 57.8 69.6 77.0 84.4 85.9 54.8 68.1 74.1 80.0 81.5 59.3 65.2 63.7
In-stent attenuation (HU) 400.1± 61.5 223.9± 25.5 204.5 ± 19.4 191.6 ± 28.0 189.7±29.1 383.6± 97.1 226.8± 8.4 195.1± 22.1 175.6 ± 33.6 172.2 ± 35.7 246.0±78.1 318.0± 39.0 226.7 ± 60.2
Tube attenuation outside
stented area (HU)
274.2± 66.8 151.1± 31.8 126.1 ± 24.7 109.7 ± 17.2 107.2±16.1 237.6±119.5 148.3 ± 22.7 130.2 ± 4.8 119.0±10.2 117.2± 12.0 200.0±9.5 231±6.1 172.7± 20.6
Noise (HU) 75.0± 2.9 32.9±1.3 26± 1.1 23.2± 0.8 24.1 ± 1.0 245.6 ± 3.6 47.4 ± 0.9 52.8 ±1.7 72.0±2.4 75.9 ± 2.5 62.0 ± 3.0 62.7 ± 1.2 40.7 ±5.8
CNR 5.4 6.7 7.8 8.1 7.4 1.6 4.8 3.6 2.4 2.2 3.9 5.1 5.6
3.00 mm
Stent lumen (mm) 1.9± 0.1 2.2± 0.1 2.3 ± 0.1 2.4 ± 0.1 2.5 ± 0.1 2.0 ±0.1 2.1±0.2 2.2±0.1 2.3± 0.1 2.3 ± 0.1 2.0 ± 0.2 2.1±0.1 2.1±0.1
Mean lumen visibility (%) 64.4 74.4 76.7 81.1 82.2 65.6 71.1 74.4 75.6 76.7 65.6 68.9 68.9
In-stent attenuation (HU) 326.5± 261.9 222.2 ± 74.9 209.7 ± 37.0 207.5±29.6 206.5± 31.4 221.5 ± 122.1 198.6 ± 35.8 214.2 ±22.2 223.8±18.3 225.4±18.3 317.7 ± 88.6 229.3 ± 30.4 225.7 ± 46.9
Tube attenuation outside
stented area (HU)
350.1± 18.6 193.6 ± 16.7 161.1±11.0 140.1± 6.2 136.5 ± 5.5 312.3 ±27.0 176.7±9.7 149.3 ± 6.6 132.5 ± 5.1 129.5 ± 4.9 189.7±5.6 205.3± 9.1 197.7 ± 27.1
Noise (HU) 105.9± 7.1 45.5 ± 2.4 35.8 ± 2.1 31.8±2.4 32.3± 2.7 245.6 ± 8.2 47.4 ± 1.8 52.8 ±2.2 72.0±2.9 75.9± 3.0 100 ± 2.0 58.7 ± 2.9 42.3 ±1.5
CNR 3.1 4.9 5.8 6.5 6.4 0.9 4.2 4.0 3.1 2.9 3.2 3.9 5.3
3.5 mm
Stent lumen (mm) 2.7± 0.1 3.1± 0.1 3.0 ± 0.2 3.2 ± 0.1 3.2 ± 0.1 2.8 ±0.1 3.0±0.1 3.1±0.1 3.1± 0.1 3.2 ± 0.1 2.9 ± 0.1 3.0±0.2 3.0±0.1
Mean lumen visibility (%) 76.2 88.6 86.7 91.4 92.4 79.1 84.8 88.6 89.5 90.5 83.8 84.8 86.7
In-stent attenuation (HU) 292.1 ± 100.8 225.3 ±12.1 198.5± 9.5 191.8± 17.9 190.6 ± 19.4 376.7 ± 125.2 234.0±11.2 205.2±20.9 187.5± 34.8 184.4 ± 37.2 242.7 ± 10.5 210.7 ±23.1 215.7±11.4
Tube Attenuation outside
stented area (HU)
316.6± 82.6 204.4± 20.1 162.4 ± 17.7 145.6 ± 15.7 143.6±14.5 262.9±84.5 186.0±4.9 170.5±21.4 161.0 ± 32.2 159.3 ± 34.0 211.0±25.7 212.3±13.6 160.3±6.0
Noise (HU) 110.5± 12.1 47.7± 4.0 37.7 ± 2.7 33±2.0 33 ± 1.9 245.6± 22.3 47. ± 4.5 52.6±3.5 71.0 ± 4.9 75.3 ± 5.1 75.7 ± 2.3 60±4.4 41.7 ± 3.1
CNR 2.8 4.7 5.3 5.8 5.7 1.6 4.9 3.8 2.6 2.4 2.8 3.5 5.2
Mono+: Advanced monoenergetic algorithm, Mono: standard monoenergetic algorithm, HU: Hounsfield units, mean value± standard deviation
1874 Eur Radiol (2016) 26:1871–1878
Discussion
By combiningthe use of a third-generation dual-source DECT
system equipped with a fully integrated circuit detector system
andanadvancedMEreconstructionalgorithm,wewereable
to demonstrate improved in-stent lumen visualization in com-
parison with standard ME and SE data-sets in stents with a
diameter of 2.25 and 3.0 mm.
Improvements in stent lumen visibility were less pro-
nounced for the 3.5 mm stent, which correlates with previous
studies describing how the effects of imaging refinements be-
come marginal for stents larger than 3 mm [16]. Stents with a
diameter <3 mm are more likely to be too small to evaluate
[17–19] and guidelines generally do not recommend the use of
CCTA for their assessment [20]. The applications of our initial
findings to clinical practice could therefore expand the indica-
tions for CCTA to include small stent assessment.
In addition, the advanced ME reconstruction algorithm al-
lows for significant improvement in iodine CNR in
Fig. 2 Lumen visibility, noise and contrast-to-noise ratio (CNR) plotted
against tube potential for each stent diameter show substantially increased
in-stent diameter in advanced and standard monoenergetic images
(mono+ and mono) in comparison to single-energy images for 2.25 mm
and 3.0 mm diameter stents as well as higher CNR and slightly lower
noise levels in mono+ images. For the 3.5 mm diameter stent the im-
provements in stent lumen visibility were less pronounced
Fig. 3 Image-based advanced monoenergetic images withvirtual photon
energies of 40 keV (A), 70 keV (B), 90 keV (C), 120 keV (D), and
130 keV (E) of the 3.0 mm stent phantom in multiplanar reformats and
cross section images show better lumen visualization and reduced bloom-
ing artefacts of the stent with increasing keV levels. The same window
settings are used in A–E (bone window setting; centre/width 300/1200
HU)
Eur Radiol (2016) 26:1871–1878 1875
comparison with standard ME and SE data-sets [11–13],
which is consistent with our results and accounts for the su-
perior performance of the advanced ME reconstruction algo-
rithm in the evaluation of in-stent lumen visibility.
Iterative reconstruction algorithms contribute to improving
the visualization of the stent struts and in-stent lumen, as
shown using different algorithm generations [3,5,6,21–23].
In our study, the application of ME reconstruction algorithms
further improves the CNR and lumen visibility obtained with
the iterative reconstruction algorithm, as demonstrated in
comparison with the SE data-set.
Another important finding of our study is the effect of
differentkeV levels on lumen visibility. The bestresult regard-
ing lumen visibility and accuracy of measuring the true lumen
diameter was observed with acquisitions at 130 keV, which is
mainly attributable to the almost complete suppression of the
Fig. 4 Cross section images of
advanced (A-C) and standard (D-
F) monoenergetic images at 70,
90, and 120 keV, respectively, as
well as single-energy images at
70, 90, and 120 kV (G-I) of the
3.0 mm stent. The monoenergetic
images result in a better lumen
visualization in comparison to
single-energy images, which is
illustrated by the exemplary mea-
surements of the lumen diameter
at monoenergetic extrapolations
(90 keV, 2.4 cm for advanced
monoenergetic algorithm (B) and
2.3 cm for standard
monoenergetic images (E)) in
comparison to the 90 kV single-
energy acquisitions (H, 2.2 cm).
The same window settings are
used in A–I (bone window set-
ting; center/width 300/1200 HU)
Fig. 5 Curved multiplanar reformats and cross section images of
advanced monoenergetic reconstructions at 70 keV (A: 2.25 mm, C:
3.5 mm stent diameter) and of single-energy acquisition at 70 kV (B:
2.25, D: 3.5 mm stent diameter). The same window settings are used in
A–F (bone window setting; centre/width 300/1200 HU). For the 2.25 mm
stent diameter the lumen visualization is substantially decreased in ad-
vanced monoenergetic extrapolations (A) in comparison to the single-
energy image (B) whereas the differences between the two acquisition
modes are less pronounced for the 3.5 mm diameter stent (C and D).
However, the increased contrast-to-noise ratio of the monoenergetic im-
ages is clearly perceptible
Fig. 6 Radiation dose comparison between single-energy and dual-
energy prospective cardiac CT angiography. The slight difference in
radiation dose observed among the three different stent diameters is
due to a difference in the acquisition length. SE: single-energy; DE:
dual-energy
1876 Eur Radiol (2016) 26:1871–1878
blooming artefacts and the higher CNR observed at this ener-
getic level. However, a significant drawback of the 130 keV
dataset is that above 100 keV, the visibility of the stent itself is
increasingly reduced, making measurements more challeng-
ing. Furthermore, it has to be taken into account that high keV
levels might also lower the attenuation of calcified plaques.
On the other hand, lowering the keV levelled to a progressive
reduction in both CNR and lumen visualization, mainly due to
increasing blooming artefacts secondary to increases in the
attenuation of the metallic stent structure.
This result seems to be in consensus with a previous study
performed with single-source DECT in a limited number of
patients, where Stehli et al. demonstrated that the optimal
visualization of the true in-stent lumen was achieved using
the ME 140 keV data-set [14]. In our study, we decided to
use an upper limit of 130 keV for the ME data-set given that
stent structures were not assessable at all at higher energy
levels. However, differences in scanner technology and recon-
struction algorithms together with the significant variability in
stent types and diameters observed in the clinical population
represent substantial limitations for direct comparison of these
two investigations.
To our knowledge, our study also represents the first direct
comparison of SE acquisitions at low kV (70 and 90 kV) with
the corresponding keV data.
As a result, we observed that ME data allow better visual-
ization of stent structure and in-lumen visibility in comparison
with SE acquisition due to a significant increase in CNR and
decrease in associated blooming artefacts.
Finally, the radiation dose of the prospectively ECG-
triggered DE acquisition was 49 % less than that of the pro-
spectively ECG-triggered SE acquisition at 120 kV, and was
comparable with the 90 kV SE scan. This remarkable result
allows DECT imaging with a radiation dose comparable to
low kV cardiac SE acquisitions, which could possibly expand
the routine utilization of the technique.
Thus, the results of our study suggest that the current trend
aimed at reducing kV at CCTA could perhaps not be the ap-
propriate strategy for an optimal visualization of coronary
stents. On the contrary, the utilization of high ME levels re-
constructed from a DE acquisition could improve the in-stent
visibility with a significant reduction in radiation dose com-
pared with standard 120 kVacquisition.
The findings of this investigation should be analyzed in the
light of its limitations. A major limitation is the phantom-
based approach and further investigations in vivo are neces-
sary to validate the clinical applicability of our results. Sec-
ondly, we did not increase keV levels beyond 130 keV, as
visibility of stent struts and stent structure markedly decreased
above 100 keV and the measurement of the lumen diameter
became imprecise. Furthermore, we investigated only one
stent type of each diameter and only strength 3 of the iterative
reconstruction algorithm. It has been reported that stent lumen
visibilityvaries significantly depending on the stent type, stent
manufacturer, and stent material [24,25], thus, our results are
only valid for the tested drug-eluting stent systems in the in-
vestigated set-up. Furthermore, the calculation of lumen visu-
alization values can be inaccurate, especially if the stent is not
fully expanded, and stent parameters were measured manual-
ly, so both values may be influenced by a certain degree of
error in measurements.
In conclusion, third-generation dual-source DECT with ad-
vanced monochromatic reconstructions substantially im-
proves the in-lumen visibility of small stents in comparison
with standard monoenergetic and single-energy CT data sets.
In addition, with this approach, the use of high keV levels
significantly improves lumen visualization by reducing
blooming artefacts.
Acknowledgments The scientific guarantor of this publication is Carlo
N. De Cecco. The authors of this manuscript declare relationships with
the following companies: Dr. Schoepf is a consultant for and receives
research support from Bayer, Bracco, GE, Medrad, and Siemens. Mr.
Canstein is a Siemens employee. The authors state that this work has
not received any funding. No complex statistical methods were necessary
for this paper. Institutional Review Board approval was not required
because the study was performed by using a thoracic phantom model.
No study subjects or cohorts have been previously reported. Methodolo-
gy: prospective, experimental, performed at one institution.
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